Tetracycline is known to concentrate and be retained in some malignant tissue relative to normal tissues. 7-Tritiotetracycline, normal tetracycline with a triton replacing a proton on the 7-carbon position, may be prepared at very high specific activity and purity. Preliminary work by the above investigators has shown anti-tumor effects of tritiotetracycline radiochemotherapy in spontaneous mammary adenocarcinomas in rats. The objective of this research is to investigate the potential therapeutic efficacy of 7-tritiotetracycline in this and other rodent malignancies. Additional studies involve: 1) the pharmacodynamics of tetracycline in normal rodents; 2) determination of tetracycline concentration and retention properties of rodent malignancies; 3) optimization of dosing regimes of tritiotetracycline in tumor suppression; 4) control studies in tumor-bearing rodents using tetracycline and tritiated water; 5) studies of acute and subacute toxicity levels of tritiotetracycline in normal rodents; 6) chemical extraction and fluorometric assay of tetracycline content of human tissue; and 7) cellular-level studies of tetracycline behavior using flow systems analysis techniques.